FOR CRIMINOLOGY CHAPTER 1-INTRO TO FORENSIC CHEM-LECTURE

Forensic Chemistry Forensic science is the application of scientifi c principles to matters involving the law. This area of science is generally considered quite fascinating and it continues to experience growing popularity. Many would agree that the current public interest in forensics is a direct result of CSI-related television programming. These weekly shows have brought a once relatively unknown area of science to the forefront of public mainstream. Viewers are captivated and intrigued by well-informed scientists working in spotless labs with ominous lighting and a modern music background. The use of cutting-edge technology provides last-minute revelations culminating in the solution of a complex crime. These programs are entertaining and have certainly increased public awareness to the fi eld of forensics; but alas, television is not reality. Although it is true that forensic science has experienced tremendous growth, few would (or should) believe this to be the result of fi ctional television programming. Media coverage of high-profi le cases has increased over the last decade in both numbers and content. Crime-scene investigation and forensic analysis have been brought out of the lab and into the public’s “scrutinizing eye.” Forensic science, once a broad fi eld, has become segregated into highly specialized disciplines. For example, forensic chemistry, forensic pathology, forensic dentistry, forensic entomology, and forensic DNA analysis have evolved into independent fi elds of forensics. It seems more appropriate – and clearly more realistic – to attribute the unprecedented popularity of forensic investigation to enhanced public awareness and an increase in the availability of career opportunities. Chemistry is the study of the composition of matter and the changes it undergoes. Forensic chemistry is a specialized area of forensic science involving the application of chemical principles and techniques to the fi eld of forensic investigation. The role of forensic chemistry in criminal investigations is vast and ranges from techniques used to collect and preserve evidence, to complex chemical procedures used to identify elements and compounds. Identifi cation procedures are highly reliable and are frequently based on the chemical and physical properties of the substance supported by data obtained from analytical analysis. Most chemical techniques used for isolation, purifi cation, and identifi cation are valid forensic techniques; however, chemical analysis differs from forensic chemical analysis in two ways: regulatory and judiciary. The results of forensic investigation may have a serious impact on lives. Therefore, techniques performed during forensic analysis must be closely regulated to ensure the accuracy and integrity of experimental results. Forensic laboratories must develop two operating manuals designed to meet the specifi c needs of each laboratory. The technical procedures manual outlines the step-by-step details of all procedures used in forensic examinations. The quality- control manual is designed to maintain the highest standards of reliability and integrity of work done by scientists in the lab. Adherence to both the technical procedures manual and lab quality manual is a crucial part of any analysis and is strictly enforced both internally and externally. Internal quality control includes, but is not limited to, periodic instrument calibration, checking reagents for expiration, and performance evaluations on scientists working in the laboratory. In addition, a detailed record is kept of all internal quality procedures performed. Outside regulatory agencies are responsible for external quality control and these agencies may vary from state to state in the US. The American Society of Crime Laboratory Directors (ASCLD) has recently accepted the painstaking task of regulating various fi elds within forensic science worldwide. This includes the forensic chemistry section in the United States. ASCLD is the regulatory organization responsible for supervising, evaluating, and directing all laboratories within its membership. Their designated inspectors evaluate technical staff and conduct periodic site inspections to ensure the highest standards of quality and technical performance. The efforts of ASCLD have helped to streamline and 4 1 Introduction standardize forensic analytical techniques worldwide. In addition, ASCLD provides direction and qualifi ed solutions to potential issues facing member laboratories. Courtroom presentation of scientifi c principles and techniques used during forensic examination is the judiciary responsibility of the forensic chemist. Forensic chemists are often called upon to describe complex chemical procedures to individuals who have a limited understanding of scientifi c principles. This responsibility can present a variety of challenges to the forensic chemist as an expert witness. Courtroom testimony is carefully prepared using common terminology and the presentation must be in a clear, simple manner that avoids confusion and misinterpretation. To achieve this, forensic chemists often use common analogies to describe complex chemical and analytical techniques. For example, a gas chromatograph is an instrument used to separate a gaseous mixture into individual components based on size and/or charge. The description of how a gas chromatograph functions may contain a reference to coin-separating machines frequently found in local grocery stores. A coin machine separates the mixture of coins based on size, and totals each pile based on weights. This analogy would illustrate how a gas chromatograph functions and may help members of a jury be more comfortable with testimony about this complex instrument. Similar analogies will be used in the following chapters to describe complex chemical procedures and analytical techniques frequently used in forensic chemistry. These analogies are designed to promote an understanding of the topic under discussion while adding clarity and continuity to the subject. 1.2 Scientifi c Investigation Imagine yourself in a classroom for an extended period of time without the ability to see outside. When you exit the building, you immediately notice that the ground is wet. Your fi rst thought is that it rained while you were inside. To confi rm this, you look to the sky to identify rain clouds. If the sky is cloudy, you are reasonably sure that it rained. If the sky is clear, you consider another possibility – perhaps sprinklers wet the ground. To confi rm this, you look for sprinklers in the immediate area. If they are found, you are reasonably sure of why the ground is wet. If no sprinklers are found, you consider another possibility and the cycle repeats. Each time you consider a possible cause, you search for supporting evidence to confi rm that cause. You accept or reject a possibility based on the presence or absence of supporting evidence. In the above scenario, you observe a water truck spraying an adjacent construction site. You are now reasonably sure of how the ground became wet. The wet ground was your observation . The possibility of rain was your fi rst hypothesis . Searching the sky for clouds was your experimentation . The absence of clouds in the sky caused you to reject your hypothesis . Other hypotheses were considered and subsequently rejected based on a lack of supporting evidence. Finally, the water truck hypothesis was confi rmed when you saw the truck in the immediate area. Your determination that the water truck wet the ground is your conclusion or theory . This deductive procedure is termed the scientifi c method : the process used to form theories . It begins with an observation : the discovery and recognition of some type of unexplained phenomenon. The observation is followed by the hypothesis : the proposal of a possible cause of the observation. The hypothesis is tested during the experimentation phase using experiments specifi cally designed to prove the hypothesis. If experimental results do not support the hypothesis, another possibility is considered and tested. If the experiments are successful and repeatable, the hypothesis becomes a theory and is presented to the scientifi c community. 1.3 Forensic Investigation Imagine a distant planet, similar to earth, with diverse climates and distinctly different environments across its surface. Now imagine that four space programs on earth send their astronauts to the new planet that, by chance, land in different regions characterized as a desert landscape, a tropical rainforest, a frozen landscape, and mountainous landscape. The astronauts explore their regions collecting samples, data, and video from their distinctly different environments. They return to their respective countries with a description of the planet supported by evidence collected during exploration. Each space program presents their information to the world, but the views are confl icting. Each country defends their position and accuses the others of presenting false or misleading information. Whom do you believe? Intuitively, you trust your astronauts and reject the other three despite the fact that, in reality, each is truthful and correct. It is not uncommon for different forensic scientists to arrive at different conclusions after examining the same piece of evidence. This is acceptable, if not expected, in the fi eld of forensic investigation. The results of forensic examinations must never be accepted or rejected because you know or trust one scientist more than another. You must keep an unbiased, open mind, knowing that two or more scientists may present different perspectives when evaluating the same piece of evidence. 1.5 Physical Properties 5 An unfortunate aspect of forensic investigation is that the results of your examination will always have a negative impact on one party. If the evidence supports the suspect’s innocence, the victim is unhappy; if it supports the suspect’s guilt, the suspect is unhappy. This is both unfortunate and unavoidable; however, it is the duty of the forensic chemist to present the unbiased story of the evidence. 1.4 Properties of Matter Matter is anything that has mass and occupies space. It is diffi cult to imagine something that has mass that does not occupy space, or something that occupies space that does not have mass. Do not spend too much time pondering the previous, I cannot think of anything either (perhaps something on the previously referenced imaginary planet). Despite the apparent redundancy in the defi nition of matter, it must satisfy the two parameters. There is a difference between the mass of an object and its weight. Weight is a force resulting from the pull of gravity on a given mass. Mass is defi ned as a specifi c quantity of matter and is not affected by the pull of gravity. The weight of an object on earth will be different from its weight on the moon because the force of gravity is different. The mass of an object will be constant at these locations despite the differences in gravitational fi eld strength. For this reason, the term “mass” should always be used in any area of science when referring to “weight.” There are three states (or phases) of matter: solid, liquid, and gas. Solids have a defi ned volume and a fi xed shape ; liquids have a defi ned volume and undefi ned shape – they conform to the shape of their container; and gases have an undefi ned volume and undefi ned shape – they take the shape and volume of the container holding the gas. Elements are the fundamental building blocks of all matter . The symbols used to identify all known elements can be found on the periodic table, an arrangement of the elements based on atomic properties. For example, “H” represents the element hydrogen and “O” represents the element oxygen. Compounds are formed through the combination of two or more elements . Chemical formulas are used to represent compounds. They specify the identity and relative number of each atom present using symbols from the periodic table and subscripts attached to each symbol. For example, the chemical formula for water is H 2 O, a compound containing two atoms of the element hydrogen (note subscript 2 attached to H) and one atom of the element oxygen. Elements and compounds may exist as pure substances or as mixtures. Pure substances contain only one component and have the same composition throughout, for example, pure gold, pure sugar, and pure water. Mixtures contain two or more pure substances and may be homogeneous or heterogeneous. Homogeneous mixtures have the same composition and properties throughout . They are not pure substances because they contain more than one component. For example, pure sugar water is a homogeneous mixture containing sugar and water. It has the same sweetness throughout; however, evaporating one component (the water) will produce the other (sugar crystals). Heterogeneous mixtures have distinctly different properties within the mixture ; water and sand would be an example. The sand and water are easily identi- fi ed, regardless of the degree of mixing. There are fundamental properties associated with all forms of matter. These distinguishing characteristics may be physical or chemical in nature and are frequently used to identify and classify a particular substance.